High-temperature article



I. 31, I950 P. A. JENNINGS HIGH-TEMPERATURE ARTICLE Filed May 5, 1948INFLUENCE OF SILICON CONTENT OF CHROMIUM NICKEL-COBALT STAINLESS STEELON CORROSION RESISTANCE IN MOLTEN LEAD OXIDE.

SAMPLES OF 20% CHROMIUM I591.- N|CKEL-'I5"/., COBALT STAINLESS OFDIFFERING SILICON CONTENTS TEMPERATURE I675 F FOR ONE HOUR SPECIMENSFLOATING IEIGHT LOSS IN GRA S/ SQ. DECJ HOUR .40 .60 .80 L00 SILICONCONTENT IN PERCENT INVENTOR. PAUL A. JNNIGS HIS ATTORNEY Patented Jan.31, 1950 $496,246 HIGH-TEMPERATURE Paul A. Jennings,

Baltimore, Armco Steel Corporation,

MIL, Basis-nor to a corporation of Ohio Application May 5, 1948, SerialNo. 25,109

7 Claims. (Cl. 75-128) I This invention relates to high temperaturestainless steel articles, especially to articles in the An object of myinvention is the provision of strong, tough and durable austeniticstainless Steel valves and valve parts for high temperature use,-whlchoffer substantial resistance to corrosion-in the heated condition inatmospheres such tures encountered by the valves frequently are as highas 700 F. or more at the fuel intake position. and as high as 1100 F. ormore at the the exhaust valves operate.

In most instances, low-alloy steel valves today are unsatisfactory inlntemal combuston engines,

components, which in view of frequent replacement. While hot, theworking parts commonly develop heat oxide scale, which detrimentallyafl'ects proper seating. In turn, failure to seat allows leakage orblow-by of the hot gases, thus increasing the valve temperature andburning away of the metal. An example of this type valve is onecontaining about 0.45% carbon, 8.50% chromium, 3.25% silicon, and theremainder substantially all iron.

A great number of the low-alloy steel valves have a low hot hardnessvalue, and thus often are susceptible to deformation while hot as underthe pounding eflects of operation. Many of the products too are highlysusceptible to creep at elevated and, accordingly, introduceinditionally, a great majority of relatively highalloy steel valves andparts likewise sufler great detriment and rapid deterioration whenexposed to the combustion products of leaded fuels.

Quite some few valves and other internal comappreciated more fully Thereare other valves in the prior art among which are those of austeniticchromium-nickel stainless steel grade. The amounts of silicon in theconventional austenitic steel products ranges from about 0.50% theaustenit c stainless steel valves have a more respect, freedom fromvolume changes and any resulting tendencies such as warping. sticking orcracking during the heating and cooling cycles brought about by the heatengine and its operation. Many valves of this 3 the prior art, however,leave much resistance to corrosive attack by lead compounds. There aremany others which, despite the general merits of austenitic steels, fallon the inferior side with respect to hot hardness and resistance tocreep.

An outstanding object of my invention accordingly is the prevision ofhigh-temperature, heatresistant, corrosion-resistant stainless steelvalves, valve parts, and other internal combustion engine componentshaving substantial strength at elevated temperatures of use includingresistance to creep, which are substantially free of phasetransformation, are hot hard, and eihciently and reliably resistoxidation in the presence of heat and leaded fuel combustion products.

Referring now more particularly to the practice of my invention, Iprovide low-silicon, austenitic chromium-nickel-cobalt stainless steelhigh temperature products, as for example internal combustion engineintake or exhaust poppet valves, valve stems or heads, seats, balls,plungers, cores and springs, valve or cylinder cladding's, linings orsurfacing, or any of a host of other internal combustion enginecomponents made of the steel. My products advantageously include about0.05% to 1.5% carbon, from 12% to 25% chromium, 2% to 25% nickel, from3% to 30% cobalt, and amounts of this element approximating 15% beingpreferred, from very small quantities up to about 0.20 silicon, and theremainder substantially all iron. By keeping an appreciable cobaltcontent in the steel, and the silicon content below about the 0.20%figure, I find sharp improvement in the resistance of the steel productsto corrosion and attack by products of combustion resulting from theburning of leaded fuel. At about 0.10% silicon and on down substantiallyto zero per cent, this improvement is even more pronounced. The smallelquantities of silicon accordingly are usually preferred.

The cobalt addition importantly dispels an adverse effect of nickel oncorrosion resistance in the presence of not lead compounds. In being anaustenite-former, the cobalt assists the maintenance of an austeniticbalance of the steel. Also, the element, in the amounts employed, im-

character in to be desired 0! proves the hot hardness and hightemperature a stretch resistance of the steel products. On occasions, Iuse nitrogen in amounts up to about 0.30% as a substitute for anequivalent amount of carbon, nickel or cobalt in the steel. The nitrogenthus serves as an austeniteformer. It also tends to increase smalldegree.

The element manganese in my high temperature chromium-nickel-cobaltstainless steel products, preferably ranges from substantially zero inamount up to about 2%. The relatively large quantities within this rangeconveniently serve as a partial substitute for such austenite-formingelements as cobalt and nickel, thus to maintain the austenitic balance.There are occasions too where my stainless steel products include in thealloy composition thereof, as for special purposes, one or more suchelements as molybdenum, titanium, columbium, tungsten, vanadium, copper,tantalum, aluminum, zirconium, or the like, ranging from quite smallamounts to substantial amounts not inconsistent with properties desired.

The stainless steel valves, valve parts, and other internal combustionengine components which I provide have a phosphorus content prefthemetal hot hardness a about 0.04%, and a sulphur content which amounts toless than 0.04%, or even as much as 0.5% or more. The largerquantitlesof sulphur, and especially those between about 0.15% to 0.50%,contribute cobalt and the low-silicon content in promoting resistance toattack by the combustion products of leaded gasolines and the like. Thelarger quantities of sulphur, say those much beyond 0.50% oftenintroduce hot working diiilculties with certain of the austenitic steelswhich I employ; also, the rate of improvement in resistance to corrosionby lead oxide usually decreases for these greater amoun My internalcombustion engine valve products and the like, in containing chromium,nickel. cobalt and the very small quantities of silicon below about0.20% have excellent heat resistance and resistance to oxidation at thehigh temperatures of operation. Also, the presence of cobalt and therestriction of silicon to the critically small amounts indicatedimportantly contribute erably below to corrosion-resistance of theproducts in the combustion products of leaded fuels, as where thestainless steel takes the form of an exhaust valve or part exposed toaircraft, truck or passenger car anti-knock fuel exhaust gases. Mystainless steel valves and other components of the steel, where made forpurposes of operation under stress at high temperatures are resistant tocreep. The metal is hot hard and stron and resists scour and abrasionwhile heated. By virtue of the austenitic quality of the steel, my valveproducts sufier substantially no phase transformation during heating andcooling cycles, and, accordingly, are free of volume changes anddifliculties often following upon change of phase. The valves resistscaling, warping and cracking at full temperature and uponbeing cooledand re-heated.

In the accompanying drawing, the approximate effect of different amountsof silicon on corrosion-resistance of 20% chromium, 15% nickel, 15%cobalt stainless steel in molten lead oxide is graphically illustrated.The carbon content of the several steel compositions concerned, isanywhere from about 0.05% to 0.10%, manganese about 0.5%, and sulphurand phosphorus each less than about 0.04%. Thus, the curve in thedrawing is directed to steels which contain chromium, nickel, cobalt,manganese, sulphur and phosphorus in substantially the constant amountsnoted, but each of the steels contains a different quantity of siliconas indicated below in the table, the remainder being substantially alliron. In this table, as in the accompanying drawing, the influence ofsilicon content on resistance in molten lead oxide for each steel isgiven in terms of grams weight loss per square decimeter per hour, for acorresponding temperature of 1675 F. of the molten lead oxide.

TABLE to the effect of the v It be observed that the Steels A and B aresteels falling within the scope of the present invention, the siliconcontent being sufliciently low,

to around 0.20%, as to the amount in the Steel B, a sharp improvementoccurs in the resistance to lead oxide corrosion.

Thus it Will be seen that in this invention there are provided a widevariety of low-silicon austenitic chromium-nickel-cobalt stainless steelarticles and products, in which the various objects noted hereinbeforetogether with many thoroughly practical advantages are successfullyachieved. It will be noted that the products are Well suited forresisting corrosion in the presence of combustion products of leadedfuels.

While certain of the steels which I provide take the form of internalcombustion engine components, it will be understood that certainadvantages of the invention are had with other products of thelow-silicon steel, amongwhich are hightemperature gas turbine nozzles,turbine parts adjacent to the nozzle, and any of a number ofsupercharger components.

As many possible embodiments may be made of my invention, and as manychanges may be made in the embodiment hereinbefore set forth, it

as a limitation.

I claim:

1. Stainless steel having great hardness at high temperatures and lowstretch in combination with substantial resistance to corrosion in thepresence of leaded fuel combustion products, and containin about 0.05%to 1.5% carbon, 12% to chromium, Irom 2% to 25% nickel, 3% to 30%cobalt, all in such proportions as to assure a substantially fullyaustenitic structure, silicon not exceeding about 0.20%, and theremainder substantially all iron.

2. Stainless steel having great hardness at high temperatures and lowstretch in combination with substantial resistance to corrosion in thepresence of leaded fuel combustion products, and containing about 0.05%to 1.5% carbon, 12% to 25% chromium, from 2% to 25% nickel, 3% to 30%cobalt, all in such proportions as to assure a substantially fullyaustenitic structure, silicon not exceeding about 0.10%, and theremainder substantially all iron.

3. Stainless steel having great hardness at high temperatures and lowstretch in combination with substantial resistance to corrosion in thepresence, of leaded fuel combustion products, and containing about 0.05%to 1.5% carbon, 12% to 25% chromium, from 2% to 25% nickel, 3% to 30%cobalt, all in such proportions as to assure a substantially fullyaustenitic structure, 0.15% to 0.50% sulphur, phosphorus not exceeding0.04%. silicon not exceeding about 0.20%, and the re maindersubstantially all iron.

4. Austenitic stainless steel internal combustion engine valves havinggreat hardness at high temperatures and low stretch in combination withsubstantial resistance to corrosion in the presence of leaded fuelcombustion products, and containing about 0.05% to 1.5% chromium, from2% to 25% nickel, 3% to 30% cobalt, silicon not exceeding 0.20%, up to0.50% sulphur.,phosphorus not exceeding 0.04%, and the remaindersubstantially all iron.

5. Austenitic stainless steel internal combustion engine valves havinggreat hardness at high temperatures and low stretch in combination withsubstantial resistance to corrosion in the presence of leaded fuelcombustion products, and containing about 0.05% to 1.5% chromium, from2% to 25% nickel, 3% to 30% cobalt, silicon not exceeding 0.20%, up to2% manganese, and the remaindersubstantially all man.

6. Austenitic stainless steel containing at least about 0.05% to 1.5%carbon, about 20% chromium, approximately 15% nickel, about 15% cobalt,silicon not exceeding about 0.20%, and the remainder substantially alliron.

7. Austenitic stainless steel internal combustion engine valves,containing about 0.05% to carbon, about 20% chromium, approximately 15%nickel, about 15% cobalt, silicon not exceeding about 0.10%, and theremainder substantially all iron.

PAUL A. JENNDIGS.

REFERENCES CITED UNITED STATES PATEN'IS Number Name Date 1,150,113Haynes Aug. 17, 1915 1,190,562 Henderson July 11, 1916 1,522,813Etchells Jan. 13, 1925 2,163,561 Payson et al June 20, 1939 2,397,034Mohling Mar. 19, 1946 FOREIGN PATENTS Number Country Date 562,102 FranceNov. 5, 1923 653,900 France Mar. 28, 1929 OTHER REFERENCES MetalsHandbook, 1939 edition, page 4'7. Published by the American Society forMetals, Cleveland, Ohio.

Chemical Abstracts, volume 28, column 3374. Published by The AmericanChemical Society at Easton, Pa.

1. STAINLESS STEEL HAVING GREAT HARDNESS AT HIGH TEMPERATURES AND LOWSTRETCH IN COMBINATION WITH SUBSTANTIAL RESISTANCE TO CORROSION IN THEPRESENCE OF LEADED FUEL COMBUSTION PRODUCTS, AND CONTAINING ABOUT 0.05%TO 1.5% CARBON, 12% TO 25% CHROMIUM, FROM 2% TO 25% NICKEL, 3% TO 30%COBALT, ALL IN SUCH PROPORTIONS AS TO ASSURE A SUBSTANTIALLY FULLYAUSTENITIC STRUCTURE, SILICON NOT EXCEEDING ABOUT 0.20%, AND THEREMAINDER SUBSTANTIALLY ALL IRON.